Hi i have the same problem on my fiat ducato.
I remove my motor only today and the fault is with the 3 wires going into the motor of which go to the brushes.
I beleive the problem on mine to be the brushes have worn down. and on moving the wires they make contact.
Try to find out if it poss to by the brushes from somewhere.
You only need a 10mm and 13mm spanner toremove.
3 bolt hold the motor in a one hold windings to motor.
james peck
January 2009